This invention relates to a moisture drain bush for an engine starter motor and, more particularly, to a moisture drain bush adapted to be inserted into and held by a moisture drain hole defined in a housing wall of an engine starter motor.
FIG. 1 illustrates one example of a conventional moisture drain bush attached to an engine starter motor. In FIG. 1, a stater motor 1 comprises a d.c. motor 2, an overrunning clutch unit with a pinion (not shown) disposed within a front bracket 3 and a solenoid switch unit 4 disposed above the motor 2 and the clutch unit. The d.c. motor 2 includes a yoke 5 and a rear bracket 6 mounted to the yoke 5 for rotatably supporting a rear end of a rotary shaft 8 of the motor 2 through a bearing 7. The motor 2 further includes a commutator 9 which is in sliding contact with a brush assembly 10 supported from the rear bracket 6. The rear bracket 6 has formed therein a moisture drain hole 11 in which a moisture drain bush 12 is inserted and held.
In FIGS. 2 and 3, which illustrate the details of the drain bush 12 shown in FIG. 1, the drain bush 12 is a substantially cylindrical tube member comprising a main body portion 13, an upper flange 14 formed at the upper end of the main body portion 13, a lower flange 15 disposed below the upper flange 14 with a clearance or a circumferential groove therebetween for receiving therein an edge of the rear bracket 6 defining the drain hole 11. The drain bush 12 also comprises a plurality of buffer plates 16 extending radially inwardly and downwardly and alternatively from the diametrically opposite inner surfaces of the tube so that a labyrinth or a serpentine flow path is defined. The upper flange 14 has formed therein two radially extending notches 14a.
The moisture within the motor housing flows through the drain notches 14a into the drain bush main body portion 13 and flows out from the bottom end of the drain bush 12. The splashed water drops entering into the drain bush 12 from its bottom end are prevented by the buffle plates 16 from passing through the drain bush 12 and entering into the interior of the motor housing.
With the above described conventional moisture drain bush, the drain bush 12 is projecting from the rear bracket 6 by a substantial radial distance. Therefore, the degree of freedom of the installation of the starter motor is limitted and some mounting space is occupied by the projecting drain bush 12.
FIGS. 4 and 5 illustrate another conventional moisture drain bush 18 for an engine starter disclosed in Japanese Patent Publication No. 60-53787. The drain bush 18 is a generally an inverted cup-shaped member made of an elastic material and comprises a top wall 18a having a downwardly extending partition wall 18b, a tubular side wall 18c having formed therein a pair of openings 18d at diameterically opposite positions and a flange 18e radially extending from an open end 18f of the side wall 18c. The drain bush 18 is elastically attached to the drain hole 11 of the housing wall 6 by the flange 18e and the circumferential groove 18g formed in the side wall 18c.
With the drain bush 18 illustrated in FIGS. 4 and 5, the height of the portion of the drain bush 18 that projects from the outer surface of the housing wall 6 is very low as compared to that of the drain bush 12 illustrated and described in conjunction with FIGS. 1 to 3. However, as shown in FIG. 5, while the water splash flying in the horizontal direction as shown by an arrow A is prevented from entering into the interior of the motor housing 6, the water splash from the below as illustrated by arrows B and C can often enter into the interior of the housing 6 and causes various harms to the starter motor, such as the generation of rust on various parts including the brushes, the brush springs and brush holders which can result in the malfunctioning of the starter 1.
Accordingly, a moisture drain bush 21 as illustrated in FIGS. 6 to 8 which is disclosed in U.S. patent application Ser. No. 477,376 filed on Feb. 9, 1990 assigned to the same assignee of the present application has been proposed. As illustrated in FIGS. 6 to 8, the proposed moisture drain bush 21 for use in a moisture drain hole 11 in an engine starter motor housing wall 6 comprises a stem 22 having an inner end 22a and an outer end 22b and axial length equal to a housing wall thickness and having axial grooves 22c extending between the inner and the outer ends 22a and 22b of the stem 22. The axial grooves 22c have a common bottom wall 22d which serves as a partition between two axial grooves 22c. An inner flange 23 having a flat inner surface 23a radially extending from the inner end 22a of the stem 22 and larger than the drain hole 11 is provided. The inner flange 23 also has two inner radial grooves 23d connected at their inner ends to the inner end of the axial grooves 22c in the stem 22 and radially extending therefrom to open at the outer periphery of the inner flange 23. An outer flange 24 having a flat inner surface 24a radially extends from the outer end of the stem 22 and larger than the drain hole 11 is provided. The outer flange 24 has two outer radial grooves 24d extending in the radially opposite directions and each connected at their inner ends to the outer ends of the axial grooves 22c of the stem 22 and open at their radially outer ends at the circumference of the outer flange 24 at substantially diametrically opposite positions.
Thus, when the drain bush 21 is inserted within the drain hole 11 in the motor housing 6, the axial grooves 22c of the stem and the inner and the outer radial grooves 23d and 24d of the inner and the outer flanges 23 and 24, respectively, as well as the drain hole together define two continuous but bent moisture drain paths extending through the housing wall 6. It is to be noted that two moisture drain paths are separated by the bottom wall 22d of or the partition between the two axial grooves 22c.
This moisture drain bush is advantageous in that it is simple in structure and has substantially no outwardly projecting portion and which effectively prevents ingress of water from the outside of the motor housing.
However, when a water splash or a jet of water impinges at the partition wall 22d of the stem 22 of the drain bush 21 at a greater speed, some water is reflected by the partition wall 22d and can splash back into the interior of the motor housing 6 through the inner radial grooves 23d.